Powertrain systems may include internal combustion engines and non-combustion torque machines, e.g., electric motor/generators to generate torque that can be transferred to a driveline for propulsion power when employed on a vehicle. Torque may be transferred between an internal combustion engine and an electric motor/generator via a pulley system that includes a continuous serpentine belt and one or more belt tensioners. Torque may be transferred from the internal combustion engine to the electric motor/generator or from the electric motor/generator to the internal combustion engine, depending upon operating demands.